1. Field of the Invention
The present invention relates to light emitting diodes and, particularly, to a high extraction efficiency light emitting diode.
2. Discussion of Related Art
In recent years, high efficiency light emitting diodes (LEDs) made with GaN-based semiconductors are widely used in different fields, such as display devices, large electronic bill boards, street lights, car lights, and specially in illumination fields. The light emitting diodes are environmentally friendly, have long working life, and low power consumption.
A conventional LED commonly includes an N-type semiconductor layer, a P-type semiconductor layer, an active channel layer, an anode, and a cathode. The active channel layer is disposed between the N-type semiconductor layer and the P-type semiconductor layer. The anode is disposed on the P-type semiconductor layer. The cathode is disposed on the N-type semiconductor layer. Typically, the anode is a transparent electrode. In operation, a positive voltage and a negative voltage are applied respectively to the P-type semiconductor layer and the N-type semiconductor layer. Thus, holes in the P-type semiconductor layer and electrons in the N-type semiconductor layer can enter the active channel layer and combine with each other to emit visible light.
However, the refractive index of the package material of the LED should match the refractive index of the semiconductor, otherwise the produced light gets partially reflected back into the semiconductor. In the semiconductor, the light may be absorbed and turned into additional heat, thus lowering the efficiency of the LED. This type of reflection also occurs at the surface of the package if the LED is coupled to a medium with a different refractive index such as a glass fiber or air. A large difference in the refractive indexes makes the reflection quite substantial, and this is usually one of the dominant causes of light extraction inefficiency of LEDs.
What is needed, therefore, is to provide a light emitting diode with elevated extraction efficiency.